The present invention relates generally to a system for monitoring thermal cooling in an electronic device. More particularly, the present invention relates to a sensor for monitoring the operation of a fan in a personal computer or computer based system.
A fan is a standard component in most commercial personal computers (PC's). The fan provides thermal cooling to the integrated circuits and the other critical components of the PC. Fans also are used in many other electronic devices and PC-based systems for the same reason. Without appropriate cooling, the electronic circuits and components in these devices are subject to premature failure, necessitating expensive repairs or replacement of the device itself. Because excessive temperature is so detrimental to electrical circuits and components, proper fan operation is critical to the operation and maintenance of these electronic devices. Many of the more sophisticated computer systems include thermal monitoring as part of an overall system management capability.
The computer systems that have thermal monitoring capabilities generally use either (1) a customized fan assembly with a built-in rotational sensor for detecting angular velocity of the fan or (2) a sensor positioned adjacent the fan to monitor the air flow generated by the fan. Both of these structures have inherent disadvantages.
The customized fan assembly is more expensive than the standard fan used in most PC's. In addition, because it is a special part, it is more difficult to procure the customized assembly than it is to obtain the standard fan. The typical fan that is mounted in a PC receives DC power from a two terminal interface connector located in the PC. The two terminal interface connector electrically connects the fan to a voltage source and ground, respectively. Using the customized fan assembly in a PC requires a third electrical terminal to provide an electrical output from the rotational sensor. As a result, a special three terminal interface connector is required to accommodate the electrical output from the rotational sensor. In addition, the rotational sensor provides an output signal that is frequency-based (for example, the rotational sensor provides an electrical output signal for each revolution of the fan). Before the PC can use the frequency-based signal from the rotational sensor, it must be converted to a voltage signal by a frequency to voltage converter.
The use of the customized fan, therefore, has several disadvantages. These disadvantages include (1) higher fan cost and longer procurement lead times for the customized fan than for the standard PC fan; (2) a special fan connector interface to provide a three wire terminal instead of the standard two-wire connector; and (3) a frequency-to-voltage converter circuit or processor to convert the electrical output signal from the rotational sensor to a voltage signal that can be used by the system management circuitry in the PC.
Similarly, the sensor for monitoring air flow has certain inherent disadvantages which limits its application. One limitation is that the air flow sensor must be positioned adjacent the fan in order to sense air flow. A second limitation is that air flow sensors are relatively expensive.
Using the prior art fan monitors, therefore, results in higher component and assembly costs and certain design related restrictions in the electronic device or PC. Consequently, these monitors have been used sparingly.
It would be advantageous to develop a simple, low cost fan monitoring system that can be implemented with the standard fan assembly to provide an indication of fan failure. It would also be advantageous if the fan monitoring system could be located independently of the fan. Still another advantage would be to provide a fan monitoring system that provides a voltage output signal indicative of fan failure.
These and other objects and advantages of the invention, constructed in accordance with the preferred embodiment, will be apparent from the following description.